Hybrid electro-mechanical powertrains have an electric motor and a prime mover, generally an internal combustion engine, interconnected through a planetary gear arrangement to a power output. The electric motor can be used to provide a starting motor for the prime mover. To accomplish this, a reaction mechanism must be provided for the planetary gear arrangement which will hold at least the power output stationary. As a general rule, a hydraulically actuated or manually actuated device (brake) has been provided to establish this reaction. These devices require hydraulic power which is generated by an electrically driven pump or a manually actuated linkage.
With the hydraulic drives, battery power is required for both the starter motor and the pump during these operations. The manual linkage system requires an interconnection between the operator and the transmission to permit the selection of the brake application.